Adjustable drill guide

ABSTRACT

An intervertebral disc space preparation guide comprises a first member and a second member. The first member includes a first spacer portion adapted for insertion in an intervertebral disc space and a first cutting block portion through which a first bore extends. The second member includes a second spacer portion adapted for insertion in an intervertebral disc space and a second cutting block portion through which a second bore extends. The first member is movably connected to the second member.

CROSS-REFERENCE

This application is a continuation-in-part application of applicationSer. No. 10/894,557, filed Jul. 20, 2004 and entitled “ARTIFICIAL SPINALDISCS AND ASSOCIATED IMPLEMENTATION INSTRUMENTS AND METHODS” whichclaims priority from U.S. Provisional Patent Application Ser. No.60/501,929 filed on Sep. 10, 2003, and entitled “ARTIFICIAL SPINAL DISCSAND ASSOCIATED IMPLEMENTATION INSTRUMENTS AND METHODS.”

BACKGROUND

The present invention relates to artificial spinal discs, andinstruments and methods associated with the implantation of suchartificial spinal discs.

Current spinal therapies for treating problematic spinal discs aremoving from rigid fixation of adjacent vertebrae across the problematicdisc space, such as with rods or plates, to maintaining the relativemotion of the adjacent vertebrae, such as with artificial spinal discs.For instance, an artificial spinal disc may be utilized to treatdegenerative disc disease, including a herniated nucleus pulposus and/orposterior osteophytes, which causes radiculopathy and/or myelopathy.Radiculopathy is compression of a spinal nerve root, while myelopathy iscompression of the spinal cord. Both are conditions that may result inan individual experiencing pain or tingling in the arms, legs, backand/or neck.

Current artificial spinal discs have drawbacks relating to theirfixation to the adjacent vertebrae and their ability to be revised, orremoved, after their implantation. For instance, current artificialdiscs may have special contours that need to be machined into theendplates of the adjacent vertebrae. Further, current artificial discsmay require special machining of the vertebrae and/or implantationinstrumentation to accommodate spikes, fins, or other structuresextending into the adjacent vertebrae that are used to fixate the discto the vertebrae. Additionally, current artificial discs may includebone in-growth surfaces across the entire vertebrae-contacting surface.This makes it difficult to remove the artificial disc, as is sometimesrequired, once the artificial disc is implanted.

Similarly, the associated implantation instruments and methods have anumber of drawbacks relating to their complexity or to their suitabilityfor use in more sensitive areas of the spine, such as in the cervicalspine. For instance, some implantation systems require the use of manydifferent instruments and devices to prepare the disc space and properlyinsert the artificial disc. Further, some implantation systems rely onimpacting, or hammering, features into the bone to accommodate theartificial disc. Such impaction techniques may be suitable in certainareas of the spine, like in the lumbar spine, but are not as desirablein other areas of the spine, like the cervical spine, where theproximity of the spinal cord and nerve roots would favor more delicateprocedures.

SUMMARY

In one embodiment, an intervertebral disc space preparation guidecomprises a first member and a second member. The first member includesa first spacer portion adapted for insertion in an intervertebral discspace and a first cutting block portion through which a first boreextends. The second member includes a second spacer portion adapted forinsertion in an intervertebral disc space and a second cutting blockportion through which a second bore extends. The first member is movablyconnected to the second member.

In another embodiment, a method of preparing an intervertebral discspace to receive an implant, the method comprises the step of creating anon-parallel angle between first and second vertebral endplates andinserting at least a portion of a cutting guide between the first andsecond vertebral endplates. The cutting guide includes a first membermovably connected to a second member. The method further comprises thestep of moving the first member with respect to the second member toplace the first member in contact with the first vertebral endplate andto place the second member in contact with the second vertebral endplateand the step of inserting a cutting device through a portion of thefirst member to cut a first formation parallel to the first vertebralendplate.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings provided toillustrate and not to limit the present invention, wherein likedesignations denote like elements, and in which:

FIG. 1 is a perspective view of an artificial spinal disc system;

FIG. 2 is a front view of the artificial spinal disc system of FIG. 1;

FIG. 3 is a bottom view of a second or inferior member of the artificialdisc system of FIG. 1;

FIG. 4 is a perspective view of an inner surface of a first or superiormember of the artificial disc system of FIG. 1;

FIG. 5 is a perspective view of an inner surface of a second or inferiormember of the artificial disc system of FIG. 1;

FIG. 6 is a bottom or inferior view of an inner surface of a first orsuperior member of the artificial disc system of FIG. 1;

FIG. 7 is a bottom or inferior view of an inner surface of a second orinferior member of the artificial disc system of FIG. 1;

FIG. 8 is a rear view of another artificial spinal disc system;

FIG. 9 is a cross-sectional view along line 9-9 of the artificial discsystem of FIG. 8;

FIG. 10 is a flowchart of a method of implanting an artificial spinaldisc system;

FIG. 11 is a representation of a patient positioned for spinal surgery,including a method of forming an access channel to access the naturalspinal disc and the adjacent vertebral bodies;

FIG. 12 is a representation of a method of removing the natural spinaldisc of FIG. 11;

FIGS. 13-14 are representations of a method of forming a predeterminedcontour in one or both end plates of adjacent vertebral bodies of FIG.11;

FIG. 15 is a representation of a prepared disc space following theprocedure of FIGS. 13-14;

FIG. 16 is a representation of determining a size of the prepared discspace of FIG. 15;

FIGS. 17-18 are representations of a rail cutter guide and method forforming one or more fin or rail guide channels in one or both end platesadjacent to the prepared disc space of FIG. 15;

FIGS. 19-20 are representations of a bone removal mechanism beingutilized in conjunction with the rail cutter guide of FIGS. 17-18;

FIG. 21 is a representation of a temporary fixation of the rail cutterguide with respect to one or more adjacent vertebrae using temporaryfixation members;

FIG. 22 is a representation of the prepared disc space of FIG. 15 withthe addition of fin or rail guide channels formed via the methods ofFIGS. 17-21;

FIG. 23 is a perspective view of an artificial spinal disc system and animplant inserter for holding and inserting the disc system into the discspace of FIG. 22;

FIG. 24 is a perspective view of a representation of a method ofinserting an artificial spinal disc system into the disc space of FIG.22;

FIG. 25 is a perspective view of a representation of a method ofremoving the implant inserter from the implanted artificial spinal discsystem of FIG. 24;

FIG. 26 is a front or anterior view of a portion of a spine thatincludes an artificial spinal disc implanted in the disc space of FIG.22;

FIG. 27 is a perspective view of another cutter guide according to anembodiment of the present disclosure;

FIG. 28 is a cross sectional view of a portion of the cutter guidedepicted in FIG. 27;

FIG. 29 is an environmental view of the cutter guide of FIG. 27;

FIG. 30 is a perspective view of another cutter guide according to anembodiment of the present disclosure; and

FIG. 31 is a perspective view of another cutter guide according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

The present invention relates to artificial disc systems, and methodsand devices associated with implanting these disc systems into a spine.One example of an artificial disc system is the system described in U.S.Pat. No. 6,113,637, which is hereby incorporated by reference. Theartificial disc systems provide predetermined bone in-growth areas thatallow for revising or removing the artificial disc after implantationand bony in-growth. Further, the artificial disc systems includestructural features that improve instrument accessibility in performingsuch a revision. Additionally, the artificial disc systems includestructures for stabilizing the disc within the associated vertebrae.And, the associated instruments and devices simplify the implantation ofthe artificial disc systems, as well as providing less traumaticinsertion of the systems into the disc space.

Referring to FIGS. 1-3, one embodiment of an artificial spinal discsystem 10 includes a first member 12 movable relative to a second member14 via an articulation component 17. Each of first and second members12, 14 include at least one bone-contacting surface 16, 18 for placementagainst a portion of an adjacent vertebral bone. Each bone-contactingsurface 16, 18 may include at least one bone in-growth surface 20, 22 ofa predetermined size and shape, and in a predetermined position andorientation on the respective surface 16, 18. The predetermined size,shape, positioning and orientation of bone in-growth surface 20, 22allows for a calculated amount of bone growth into the disc members 12,14 for secure fixation to the adjacent bone, while allowing for easyremoval of the disc member from the adjacent bone after bone in-growthoccurs if such removal is required at a later date by changing medicalneeds. Further, the top surface 24, 26 of bone in-growth surface 20, 22may have a predetermined spacing 28, 30 (FIG. 2) above the remainingportion of bone-contacting surface 16, 18 to allow for increasedpenetration and/or compression of the adjacent vertebral bone into bonein-growth surface 20, 22 upon implantation of artificial disc system 10.Additionally, each member 12, 14 may include at least one bone in-growtharea indicator 32, 34 that identifies the location of the bone in-growthsurface 20, 22. For instance, after artificial disc system 10 isimplanted, bone in-growth area indicator 32, 34 provides a visual markerthat can be seen by the naked eye, such as through an incision thatexposes a surface of the system 10, or by medical diagnostic equipment,such as x-ray, ultrasound, magnetic resonance, computed tomography,positron emission technology, and other such diagnostic techniques.Further, bone in-growth area indicator 32, 34 may further include aninstrument access guide 36, 38 that cooperates with a medicalinstrument, such as an osteotome, used in removing artificial discsystem 10. Instrument access guide 36, 38 directs the instrument to theexact position of bone in-growth surface 20, 22, thereby avoidingunnecessary work in non-bone-in-growth areas of bone-contacting surface16, 18 and without interfering with other structures that may be presenton surfaces 16, 18. Thus, artificial disc system 10 provides featuresfor secure fixation to adjacent vertebral bone while allowing for easyremoval of all or a portion of the system if later required by changingmedical needs.

Bone in-growth surface 20, 22 generally has a size that is substantiallyless than the overall size of the respective bone-contacting surface 16,18. Further, bone in-growth surface 20, 22 may be positioned onrespective bone-contacting surface 16, 18 such that after implantationbone in-growth surface 20, 22 is located proximal to cancellous boneportions, rather than cortical bone portions, of the adjacent vertebralbone. Such positioning, for example, may be at the center of member 12,14 for a disc system that substantially spans the disc space orvertebral endplate. Alternatively, such positioning may be off-centerwith respect to member 12, 14 if the disc system only spans a portion ofthe disc space or vertebral end plate. Additionally, bone in-growthsurface 20, 22 may be positioned at a predetermined spacing 40, 42 froman edge 44, 46 of member 12, 14 that is exposed after implantation ofthe system 10, such as an edge that is not within the disc space betweenthe adjacent vertebrae. Predetermined spacing 40, 42 allows for easierentry of an instrument, such as an osteotome, that is used to separatemember 12, 14 from the vertebral bone after bony in-growth has occurred.Furthermore, bone in-growth surface 20, 22 may lie in a single plane, ormay lie in one or more planes, which may be intersecting planes, if moresecure fixation and bony in-growth is desired. Suitable examples of bonein-growth surface 20, 22 may include surfaces that arechemically-etched, machined, sprayed, layered, fused, coated or texturedin any manner or with any material that allows for the growth andattachment of bone.

Bone in-growth indicator 32, 34 may include any type of marker, such asan indentation, an embedded marker, coatings, projections, etc., on anysurface of member 12, 14. Further, instrument access guide 36, 38 mayinclude any surface or combination of surfaces that work in cooperationwith a surface or portion of a medical instrument used from separatingmember 12, 14 from bone. Alternatively, instrument access guide 36, 38may comprise a marker to indicate a position in computer- and/orimage-guided surgery.

Further, referring to FIG. 2, securing of the artificial disc system 10to bone may be enhanced by applying a bone growth promoting substance 49to a bone contacting surface 16, 18 of the artificial disc system. Inparticular, bone growth promoting substance 49 may be applied to one ormore bone in-growth surfaces 22 to encourage bone to growth into thisarea. Suitable examples of bone growth promoting substances include bonemorphogenic protein (“BMP”), LIM mineralization protein (“LMP”),demineralized bone matrix (“DBM”), mesenchymal stem cells, bloodplatelet gel, and other similar materials.

Articulation component 17 may be a structure integral with, or separablefrom, one or both of first member 12 and the second member 14. Referringto FIGS. 4-7, for example, in one embodiment articulation component 17includes a joint 48 defined by at least a partly convex or curvilinearsurface 50, such as a substantially spherical ball, projecting fromfirst member 12 movable in at least a partly concave or curvilinearsurface 52, such as an elongated socket, formed within second member 14.Alternatively, articulation component 17 may be an entirely separatemember or combination of members, such as a ball, disc, nucleus,flexible and/or elastic component, etc., positionable in combinationwith first and second members 12, 14 to allow relative rotational and/ortranslational motion between the first and second members. Furthermore,first and second member 12, 14 and articulation member 17 may beinterconnected to form a single assembly.

Additionally, artificial disc system 10 may include at least one fin orrail member 54 projecting out of bone contacting surface 16, 18 on atleast one of first or second member 12, 14. Fin or rail member 54provides surfaces 56, 58 positioned substantially normal to bonecontacting surface 16, 18 that oppose translational or rotationalmovement of member 12, 14 within adjacent vertebral bone in a planeparallel to the surfaces 16, 18. It should be noted, however, that theparticular orientation of surfaces 56, 58 may be adjusted to resistrelative motion in any desired plane or direction. Additionally, fin orrail member 54 may include a top engagement surface 60, such as may beformed by teeth, knurling, texturing, etc., that further resistsmovement of member 12, 14 within bone. For example, for an artificialspinal disc system 10 inserted into the disc space from the anteriorside, top engagement surface 60 may resist movement of the implanteddisc in the anterior direction by allowing bone to grow or be positionedin the medial lateral direction between portions of the top engagementsurface. Surface 60 may be oriented to resist relative motion betweenmember 12, 14 and bone in a different direction, but in the same plane,as surfaces 56, 58. It should be noted, however, that surfaces 56, 58and 60 may be oriented in a manner to resist any combination ofdirections of relative motion. Additionally, top engagement surface 60,as well as surface 56, 58 may be formed with angled or other biasedsurfaces that have a greater resistance to motion in one or more desireddirections. For example, top engagement surface 60 may include aplurality of teeth defined by at least two surfaces, where at least onesurface is substantially normal to bone contacting surface 16, 18 andthe other wall is substantially non-orthogonally-angled relative to bonecontacting surface 16, 18.

Further fin or rail member 54 may lie along a line oriented parallel toan insertion direction, where the insertion direction is a direction inwhich artificial spinal disc system 10, or either individual member 12,14, is inserted into position between adjacent vertebrae. It should beunderstood, however, that fin or rail member 54 may lie along acurvilinear line, and may be angled with respect to the insertiondirection. Additionally, fin or rail member 54 may be of anypredetermined length. For example, fin or rail member 54 may be of alength greater than or less than the overall edge-to-edge length ofartificial spinal disc system 10. For instance, fin or rail member 54may be of a length such that it is spaced apart from any edge of thedisc system 10, or one or both ends of the fin or rail member may besubstantially parallel with an edge of the disc system. When an end offin or rail member 54 is parallel with an edge of disc system 10, suchas exposed edge 44, 46, then the fin or rail member may act as bonein-growth indicator 32, 34 and/or instrument access guide 36, 38.

Additionally, artificial spinal disc system 10 may include tabs 62 orother longitudinally extending members that allow the disc system to beheld with an insertion instrument. For instance, tabs 62 may include oneor more connector structures 64 (FIG. 2), such as an internal wall thatdefines a cavity or hole, that correspond with engaging features on aninsertion instrument that is utilized to hold and/or insert one or bothmembers 12, 14. Alternatively, connector structure 64 may includeprojections that extend into corresponding holes or cavities in theinsertion instrument. Further, tabs or extending members 62 may preventmovement of member 12, 14 relative to the overlapping bone afterimplantation. For example, for a disc system 10 that is inserted betweenadjacent vertebrae from the anterior side, tabs or extending members 62project away from the disc space and over the anterior portion of thevertebral body, thereby preventing relative movement of the member 12,14 in the posterior direction.

First member 12, second member 14 and articulation component 17 each maybe formed from any combination of one or more different biocompatiblematerials. Suitable materials include stainless steel, cobalt chrome,titanium, rubber, elastomer, polymers, etc., including all alloys andvariations of these materials.

Referring to FIGS. 8 and 9, in another embodiment, artificial spinaldisc system 70 may include a first member 12 movable relative to asecond member 72, where such movement has a predetermined range ofmotion 74, in at least one direction, greater than the natural range ofmotion 76 of the natural disc being replaced. For instance, in anembodiment where articulation component 17 comprises a convex surface 50interacting with a concave surface 52, the concave surface 52 may have apredetermined range of motion 74 corresponding to ananterior-to-posterior translation greater than that of the natural rangeof anterior-to-posterior translation of the natural disc being replaced.For example, for a spinal disc anterior-to-posterior translationtypically corresponds to flexion and extension movements of the spinalmotion segment, which movements would typically be constrained bynatural tissue, including muscle, tendons, annulus fibrosus and/or facetjoints. Thus, it may not be necessary to provide physical constraintswithin disc system 70 that limit the movement of first member 12 andsecond member 72, and hence articulation component 17, as the naturalstructure of the tissue adjacent the implanted artificial spinal discsystem 70 may naturally limit the relative motion of the disc system. Itshould be noted that the predetermined range of motion 74 may be in anycombination of one or more directions or planes, and may completeoverlap the natural range of motion 76, be biased toward one side of thenatural range of motion, or be within one side but extend beyond theother side of the natural range of motion. Additionally, although notrequired, artificial spinal disc system 70 may include a safety stop 78positioned outside of the natural range of motion 76 to ultimately limitthe movement of first member 12 relative to second member 72. Safetystop 78 may be formed in first member 12, second member 72 or inarticulation component 17.

Referring to FIG. 10, embodiments of a method of implanting anartificial spinal disc system includes performing pre-operative planning(Block 80), removing the existing natural disc (Block 82), preparing theintervertebral space for receiving the artificial disc system (Block84), and inserting and securing the artificial disc system (Block 86).The action of pre-operative planning may include examining the patient,taking x-rays or performing other diagnostic procedures to analyze thenatural disc at issue, analyzing and/or calculating the existing ornatural range of motion of the spinal motion segment, and/or measuringthe natural disc space at issue to determine an appropriate sizeartificial disc system. The action of removing the natural disc mayinclude a procedure such as a discectomy or partial discectomy, or anyother procedure that removes all or a portion of the natural discnucleus pulposus. The action of preparing the intervertebral space forreceiving the artificial disc system may include contouring the endplates of the adjacent vertebrae. Such contouring may include formingparallel surfaces, forming concave surfaces, or forming any other shapein the end plate to receive the artificial disc system. In particular,as will be discussed in more detail below, the action of contouring theend plates may further include machining at least one fin or railopening to receive a corresponding at least one fin or rail memberassociated with the artificial disc system. The action of machining mayinclude removing a channel of bone from the end plate using tool havinga surface adapted for removing bone, where the tool is capable ofrotating, vibrating, reciprocating or otherwise acting on the end plateto remove bone. Further, the action of inserting and securing theartificial disc system may include holding a single component or theentire assembled artificial disc system and moving it into the preparedintervertebral disc space until it reaches a predetermined desiredposition. Securing the artificial disc system may occur naturally due tothe compressive forces acting across the implanted artificial discsystem, or may occur due to the contouring of the end plates, or mayoccur due to supplemental fixation techniques such as applying a screwor other component to hold a component of the system to the vertebralbone, or may occur as some combination of these techniques. Further,securing of the artificial disc system may be further achieved byapplying a bone growth promoting substance to a bone contacting surfaceof the artificial disc system. Suitable examples of bone growthpromoting substances include bone morphogenic protein (“BMP”), LIMmineralization protein (“LMP”), demineralized bone matrix (“DBM”),mesenchymal stem cells, blood platelet gel, and other similar materials.It should be noted that the above method may be achieved through an opensurgical site, or in a minimally invasive manner such as through a tubeor channel that allows from a relatively small opening in the skin andtissue of the patient compared to the open procedure.

Referring to FIGS. 11-26, an embodiment of a method of implanting anartificial spinal disc system in the cervical portion of the spineincludes positioning the patient for surgery, performing a discectomyand decompressing the disc space, preparing the adjacent vertebralendplates, and inserting the artificial spinal disc. Referring to FIG.11, the patient 90 may be positioned such that their neck 92 is in aneutral position corresponding to the natural lordosis of the cervicalspine. After making an incision, an access channel 94 to the naturalspinal disc 96 and/or adjacent vertebrae 98, 100 may be maintained by anopener mechanism 102, such as one or more retractor blades or anendoscopic port or channel, respective examples including a TRIMLINEretractor blade or an X-TUBE endoscopic port both manufactured byMedtronic Sofamor Danek USA (Memphis, Tenn.). Then, referring to FIG.12, the natural spinal disc 96 is removed using a disc removalinstrument 104, such as a curette, osteotome or any instrumentspecifically designed for removal of all or a portion of the naturaldisc. After removal of all or a portion of the natural spinal disc 96,the disc space is decompressed, such as by using the Smith-Robinsondecompression technique.

Referring to FIGS. 13-15, after removal of the natural disc, referred toas a discectomy, and decompression, at least one contouring device 106may be utilized to form a predetermined contour 108, 110 which maygenerally correspond to the bone contacting surface of the artificialdisc, into one of both of the adjacent vertebral bodies 98, 100. Forexample, in one embodiment, the vertebral end plates are machined to beflat and parallel, such as by using a cylindrical burr. It should benoted, however, that other contouring devices 106, such as mills,cutters, saws, etc., and other predetermined shape-forming devices maybe used to remove bone from the end plates. In order to avoid subsidenceof the artificial disc system into the end plates, the machining processmay be performed to preserve as much cortical bone as possible.Additionally, referring specifically to FIG. 13, it should be noted thata reference device 112, such as a frame or such as markers, may be usedin conjunction with contouring device 106 to control or guide themovements of the contouring device. For instance, reference device 112may be attached to one or both adjacent vertebrae 98, 100 so as toprovide geometric guidance to contouring device 106. After end platecontouring is complete, then the prepared disc space 114 (FIG. 15) maybe ready for disc insertion and all external distraction may be removed.

Referring to FIG. 16, in order to determine the proper size artificialdisc to use, an implant trial 116 may be inserted determine the size ofthe prepared disc space 114. In some embodiments that desire to avoidexcessive compressive forces on the artificial disc system, the properlysized implant trial 116 fits snug in the prepared disc space 114 butdoes not distract the adjacent vertebrae 98, 100. Additionally, the fitof implant trial 116 may be confirmed diagnostically, such as withfluoroscopy. Referring to FIG. 17, once the appropriate sized implanttrial 116 is determined, the correspondingly sized rail cutter guide 118is selected and used to prepare one or more fin or rail channels in theendplates in correspondence with the fin or rail member on theartificial disc system.

Referring to FIGS. 17-22, one embodiment of a rail cutter guide 118includes at least one machining guide 120 positioned on guide body 122and having a size 124 to provide a reference to a bone cutting device126 to form a fin or rail member channel 128 in one or both adjacentvertebrae 98, 100 corresponding in position and size to the fin or railguide member on the artificial spinal disc system. In embodiments havingmore than one machining guide 120, referring specifically to FIG. 19,each machining guide 120 may have a predetermined longitudinal spacing121 and/or a predetermined lateral spacing 123 with respect one or moreof the other machining guides. Such predetermined spacing 121, 123 isadvantageous for insuring formation of at least two fin or rail memberchannels 128 (FIG. 22), either in one vertebral end plate or in adjacentend plates, that are in alignment with the predetermined spacing of atleast two or more fin or rail members on an artificial spinal discselected to be implanted. Further, rail cutter guide 118 may include aspacer portion 130 sized and having a thickness 132 (FIG. 20)corresponding to a desired disc spacing, such as the natural neutraldisc spacing of the prepared disc space 114. Additionally, guide body122 or spacer portion 130 may include predetermined recesses 131 sizedto accommodate at least a portion of a bone removal device. Rail cutterguide 118 may further include a permanent or removably attachable handle134 for manipulating the position of the guide. Referring specificallyto FIG. 17, rail cutter guide 118 may further include an engagementstructure 136, such as a protrusion or an extension, that interacts withurging mechanism 138, such as a hammer-like or moving-weight typedevice, for moving the guide 118 into proper position. Rather than, orin addition to, being referenced to the prepared disc space 114 and/orthe adjacent vertebrae 98, 100 via spacer portion 130, rail cutter guide118 may include one or more reference markers 140 so as to insure adesired positioning with respect to the adjacent vertebrae. The desiredpositioning, for example, may include a cephalad-caudal positioning, alateral positioning, a depth within the prepared disc space 114positioning, and any combination thereof. For example, reference marker140 may include a limiting structure 142 projecting from guide body 122so as to limit the depth of penetration of the guide body into prepareddisc space 114. Further, one or more reference markers 140 may beassociated with any other structure having a known position relative toone or both vertebrae 98, 100 and/or prepared disc space 114.

Referring back to FIG. 17, to position the rail cutter guide 118relative to the adjacent vertebral bodies 98, 100, urging mechanism 138may be utilized to move the rail cutter guide 118 into a desiredposition. For instance, in one embodiment, rail cutter guide 118 isimpacted until all limiting structures 142 touch the anterior surface ofthe adjacent vertebrae 98, 100. Referring to FIG. 19-22, after removingurging mechanism 138, a bone removal mechanism 144 may be movablerelative to machining guide 120 to create fin or rail member channel 128(FIG. 22). In one embodiment, for example, bone removal mechanism 144may include a drill bit 146 attachable to either an actuation mechanism148, such as a power source or a manual drill bit handle. In thisembodiment, drill bit 146 is inserted into one port formed withinmachining guide 120 on rail cutter guide 118, and operates to form onechannel 128 in the endplate. Referring specifically to FIG. 21, it maybe desired to secure the relative position of rail cutter guide 118 andthe first-formed channel 128 (not shown) in order to insure propergeometric alignment of successive channels. In such a situation, atemporary fixation mechanism 150, such as a pin or screw, may be securedto rail cutter guide 118, such as to machining guide 120. Then, thesuccessive channels 128 may be formed, and additional temporary fixationmechanisms 150 may be applied. Referring specifically to FIG. 22, afterremoving any temporary fixation mechanisms 150 and rail cutter guide118, one or both endplates should have one or more properly positionedchannels 128.

Referring to FIGS. 23-26, an artificial spinal disc system 10 or 70,such as the PRESTIGE Cervical Disc manufactured by Medtronic SofamorDanek USA (Memphis, Tenn.) may be attached onto an implant inserter 152.In one embodiment, for example, the implant inserter 152 includes fourinserter prongs 154 (only 3 are visible in FIG. 23), attached to legs155 positioned within outer sheath 156, that fit into holes 64 withintabs 62. Outer sheath 156 is advanced to apply a force across the prongs154 to hold the disc system 10 or 70. The one or more fin or railmembers 54 are aligned with one or more channels 28 on the endplates ofthe adjacent vertebrae 98, 100, and the disc system 10 or 70 is insertedinto the prepared disc space 114. Insertion may be aided by urgingmechanism 138, and disc system 10 or 70 is advanced until the anteriorlypositioned tabs 62 come into contact with the anterior surface of theadjacent vertebral bodies 98, 100. Disc system 10 or 70 may then bereleased by implant inserter 152, for example by sliding back outersheath 156 and gently removing implant inserter 152. Final placement ofdisc system 10 or 70 between adjacent vertebrae 98, 100 may be verifiedusing medical diagnostic equipment, such as by using fluoroscopy. Thesurgery may be completed using standard closure procedures.

Thus, the present invention includes various embodiments of artificialspinal discs having predetermined bone in-growth areas and additionalfeatures to aid in the removal or revision of the implanted artificialdisc. Additionally, the present invention includes various embodimentsof fin or guide rail channel-forming mechanisms, and of methods ofimplanting artificial discs having at least one fin or guide railmember.

Referring now to FIG. 27, a cutting guide 200 may be used to createtracks or holes in adjacent vertebral bodies. These tracks or holes maycorrespond in size and position to rails, fins, bone screws, fastenersor other features included in an artificial disc system. The cuttingguide 200 may include an upper member 202 and a lower member 204. Theupper member 202 may include a spacer portion 206, and the lower member204 may include a spacer portion 208. The upper member 202 may alsoinclude a cutting block 210, and the lower member 204 may include acutting block 212. The cutting blocks 210, 212 may serve as penetrationlimiting extensions. The cutting block 210 may include bores 214, 216sized to accept an instrument (not shown) such as a drill bit 146. Apredetermined spacing 217 may separate the bores 214, 216 to permitformation of two tracks or holes. In this embodiment the spacing 217between the bores 214, 216 is generally constant along the length of thebores, resulting in generally parallel tracks or holes. It is understoodthat the predetermined spacing may vary along the length of the bores tocreate nonparallel tracks or holes as the profile of the artificial discmay warrant. Similar bores may be located in the cutting block 212. Thecutting guide 200 may further include a permanent or removablyattachable handle 218 extending from the upper member 202 and a similarhandle 220 extending from the lower member 204.

In an alternative embodiment, slots or recesses, similar to recesses131, may be formed in the spacer portion 206, 208 to accommodate thepassage of at least a portion of drill bit 146 when forming rails in theadjacent vertebral bodies. In another alternative embodiment, the uppermembers and the lower members may include reference markers to insure adesired positioning with respect to the adjacent vertebral bodies. Thedesired positioning, for example, may include a cephalad-caudalpositioning, a lateral positioning, a depth (anterior-posterior) withinthe disc space, and any combination thereof.

Referring now to FIG. 28, the upper and lower members 202, 204 may bemovably connected to each other by a pivot mechanism 221. In thisembodiment, the pivot mechanism is a ball and socket type joint formedby a domed recess 222 formed in the upper member 202 and a domed capprotruding from the lower member 204. Tabs 224 and 226 may extend fromthe domed recess 222. The domed cap 228 may include an indention 230sized to allow pass through of the tab 224. A second indention 232 maybe located opposite the indention 230 and may be sized to allow passthrough of the tab 226. The upper member 202 may be connected to thelower member 204 by aligning the tabs 224, 226 with the indentions 230,232 and inserting the domed cap 228 into the domed recess 222. After thedomed cap 228 has been inserted into the domed recess 222, the lowermember 204 may be turned relative to the upper member 202 to lock thecap 228 within the recess 222 and align the upper member 202 with thelower member 204.

The spacer portions may be provided in a variety of thicknesses toaccommodate the distraction and lordotic angle used for a particularpatient, and different thicknesses may be used for the upper and lowerspacer portions. In the embodiment of FIG. 28, the spacer portion 206has a thickness 240 that is greater than a thickness 242 of the spacerportion 208.

The preferences of the surgeon and/or the condition of the patient maydetermine whether, during surgery, the patient's spine will be held in amore natural position with the targeted vertebral endplates generallyparallel or whether the patient will be placed in lordosis with thetargeted vertebral endplates angled relative to one another. When apatient is placed in lordosis, the cutting guide 200 may be used to formthe tracks or holes generally parallel to the respective vertebralendplates. For instance, in one embodiment as shown in FIG. 29, theadjacent vertebral bodies 98, 100 may be positioned relative to eachother at an anterior-posterior angle 250 which may range fromapproximately 0 to 10 degrees. Additionally or alternatively, thevertebral bodies 98, 100 may be angled in a lateral direction. With thepatient positioned at the desired lordotic angle 250, the cutting guide200 may be inserted between adjacent vertebrae 98, 100. As the cuttingguide 200 is inserted, the pivoting mechanism 221 formed by the domedcap 228 within the domed recess 222 may adjust to the angle 250. Thespacer portions 206, 208 may be inserted until the protruding cuttingblocks 210, 212 limit further insertion by touching the anterior surfaceof the vertebral bodies 98, 100, respectively.

The cutting guide 200 may be manually held in position with the spacerportions 206, 208 firmly against the endplates of the vertebral bodies.Alternatively, as shown in the embodiment of FIG. 30, a separationdevice 260 may be introduced to hold the upper member 202 and the lowermember 204 in place. The separation device 260 may include a throughbore 262, an angled leg 264, and an alignment leg 266. The handle 218may be inserted through the bore 262 and the angled leg 264 may bepositioned on a surface of the handle 220 facing the handle 218. Theangled leg 264 may move along a flat surface of the handle 220, along agroove in the handle 220, or by any other moving connection meanscontemplated by one skilled in the art. The alignment leg 266 mayprevent any unwanted lateral pivoting of the upper member 202 withrespect to the lower member 204. The separation device 260 may slidealong the handle 218 as far as possible until the device 260 pushesapart the arms 218, 220 and correspondingly pushes the upper and lowermembers 202, 204 against the endplates of vertebral bodies 98, 100,respectively.

After the cutting guide 200 is positioned, the drill bit 146 may beinserted through bore 216 to drill a hole 270 in the vertebral body 98parallel to the endplate. The drill bit 146 may then be inserted intobore 214 to drill a hole in the vertebral body 100 parallel to the hole270 and parallel to the endplate of vertebral body 98. The drill bit 146may then be used with lower member 204 in a similar manner to drillholes in vertebral body 100. It is understood that the holes may bedrilled in any sequence chosen by the surgeon. It is also understoodthat with alternative configurations of the upper and lower members, thedrill bit 146 may be used to create rails or tracks rather than holes.

Referring now to FIG. 31, in another embodiment, a cutting guide 300 maybe used to create formations such as tracks or holes in adjacentvertebral bodies. These tracks or holes may correspond in size andposition to rails, fins, fasteners or other features found on anartificial disc system. The cutting guide 300 may include an uppermember 302 and a lower member 304. The upper member 302 may include aspacer portion 306, and the lower member 304 may include a spacerportion 308. The upper member 302 may also include a cutting block 310,and the lower member 304 may include a cutting block 312. The cuttingblock 310 may include bores 314, 316 (not visible) sized to accept aninstrument such as a drill bit 146. A predetermined spacing may separatethe bores 314, 216 to permit formation of two tracks or holes. Similarbores may be located in the cutting block 312. The cutting guide 300 mayfurther include a permanent or removably attachable handle 318 extendingfrom the upper member 202 and a similar handle 320 extending from thelower member 304.

The upper and lower members 302, 304 may be movably connected to eachother by a pivot mechanism 321. In this embodiment, the pivot mechanismis formed by an upper hinge component 322 extending from the uppermember 302 coupled to a lower hinge component 324 protruding from thelower member 304. The lower hinge component 324 may include a U orJ-shaped latch which may be coupled to a shaft portion of the upperhinge component 322. A J-shaped latch may allow the lower hingecomponent 324 to become more easily separated from the upper hingeportion. A coil spring 326 may be attached between the upper member 302and lower member 304 and may exert a force to push apart the upper andlower members to create an angle therebetween. It is understood that thecoil spring 326 is only one example and that other types of mechanismssuch as screws, jacks, and inflatable bodies may be used to hold theupper and lower members 302, 304 against the respective vertebralendplates.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. For instance, all or predeterminedportions of the bone-contacting surfaces of the artificial disc systemsmay comprise bone in-growth surfaces. Accordingly, all suchmodifications and alternative are intended to be included within thescope of this invention as defined in the following claims. Thoseskilled in the art should also realize that such modifications andequivalent constructions or methods do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure. It is understood that all spatialreferences, such as “horizontal,” “vertical,” “top,” “upper,” “lower,”“bottom,” “left,” and “right,” are for illustrative purposes only andcan be varied within the scope of the disclosure. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures.

1. An intervertebral disc space preparation guide comprising: a firstmember including a body portion having: a first spacer portion adaptedfor insertion in an intervertebral disc space, and a first cutting blockportion through which a first bore extends; and an elongated handlepermanently attached to the body portion to facilitate insertion of thebody portion into a patient and removal of the body portion from thepatient; and a second member including a second spacer portion adaptedfor insertion in an intervertebral disc space and a second cutting blockportion through which a second bore extends, wherein the first member ismovably connected to the second member; wherein the first spacer portionis pivotally connected to the second spacer portion; wherein the firstspacer portion is pivotally connected to the second spacer portion by aball and socket type joint; wherein the ball and socket type jointincludes a domed shaped protrusion extending from the first member and adomed shaped recess formed in the second member.
 2. The guide of claim 1further comprising a locking mechanism for preventing the domed shapeprotrusion from separating from the domed shape recess.
 3. The guide ofclaim 1 wherein the domed shaped protrusion comprises at least oneindention and the domed shape recess comprises at least one tab andwherein the at least one tab is insertable through the at least oneindention and wherein the dome shaped protrusion is rotatable relativeto the domed shape recess after insertion of the at least one tabthrough the at least one indention to lock the first member to thesecond member.
 4. The guide of claim 1 wherein a third bore extendsthrough the first cutting block portion and a fourth bore extendsthrough the second cutting block portion.
 5. The guide of claim 4wherein the first bore is parallel to the third bore.
 6. The guide ofclaim 1 wherein the first spacer portion comprises a recess extendingfrom the first bore.
 7. The guide of claim 1 wherein the intervertebraldisc space comprises a lordotic angle between a first vertebral endplateand a second vertebral endplate and wherein the first and second spacerportions are adapted to contact the first and second vertebralendplates, respectively, at the lordotic angle.
 8. The guide of claim 7wherein the lordotic angle ranges between 0 and 10 degrees.
 9. The guideof claim 1 wherein the first and second spacer portions have differentthicknesses.
 10. The guide of claim 1 wherein the first cutting blockportion comprises a penetration limiting extension.
 11. Anintervertebral disc space preparation guide comprising: a first memberincluding a body portion having: a first spacer portion adapted forinsertion in an intervertebral disc space, and a first cutting blockportion through which a first bore extends; and an elongated handlepermanently attached to the body portion to facilitate insertion of thebody portion into a patient and removal of the body portion from thepatient; and a second member including a second spacer portion adaptedfor insertion in an intervertebral disc space and second cutting blockportion through which a second bore extends, wherein the first member ismovably connected to the second member; wherein a third bore extendsthrough the first cutting block nonparallel to the first bore.
 12. Theguide of claim 11 wherein the first spacer portion is pivotallyconnected to the second spacer by a hinge joint.
 13. The guide of claim12 wherein the hinge joint includes a shaft formed on the first spacerportion and a J-shaped latch formed on the second spacer portion. 14.The guide of claim 11 wherein a coil spring extends between the firstmember and the second member.
 15. The assembly of claim 11 wherein firstvertebral endplate forms an angle with respect to the second vertebralendplate and wherein the first spacer portion is positionable againstthe first vertebral endplate and the second spacer portion ispositionable against the second vertebral endplate.
 16. The assembly ofclaim 15 wherein the angle is between 0 and 10 degrees.
 17. The guide ofclaim 11, wherein a fourth bore extends through the second cutting blocknonparallel to the second bore.
 18. The guide of claim 11, wherein thesecond member includes an elongated handle permanently attached to atleast a portion of the second cutting block.
 19. The assembly of claim11, wherein the first spacer portion is pivotally connected to thesecond spacer portion by a domed shaped protrusion engaged with a domedshaped recess.
 20. The assembly of claim 19 further comprising amechanism for preventing the domed shape protrusion from separating fromthe domed shape recess.
 21. The assembly of claim 20 wherein the domedshaped protrusion comprises at least one indention and the domed shaperecess comprises at least one tab and wherein the at least one tab isinsertable through the at least one indention and wherein the domeshaped protrusion is rotatable relative to the domed shape recess afterinsertion of the at least one tab through the at least one indention toprevent the domed shape protrusion from separating from the domed shaperecess.
 22. A surgical cutting guide, comprising: a first memberincluding: a first body portion having: a first spacer portion sized andshaped for insertion at least partially into an intervertebral discspace between a first vertebra and a second vertebra, and a firstcutting block portion integrally formed with the first spacer portion,the first cutting block portion sized and shaped for positioning outsideof the intervertebral disc space and in engagement with an outer surfaceof the first vertebra when the first spacer portion is positioned atleast partially within the intervertebral disc space, the first cuttingblock having at least one opening extending therethrough; and a firstelongated handle attached to the first body portion to facilitateinsertion of the first spacer portion at least partially into theintervertebral disc space and to facilitate removal of the first spacerportion from at least partially within the intervertebral disc space;and a second member including: a second body portion having: a secondspacer portion sized and shaped for insertion at least partially intothe intervertebral disc space opposite the first spacer portion, and asecond cutting block portion integ rally formed with the second spacerportion, the second cutting block portion sized and shaped forpositioning outside of the intervertebral disc space and in engagementwith an outer surface of the second vertebra when the second spacerportion is positioned at least partially within the intervertebral discspace; and a second elongated handle attached to the second body portionto facilitate insertion of the second spacer portion at least partiallyinto the intervertebral disc space and to facilitate removal of thesecond spacer portion from at least partially within the intervertebraldisc space; wherein the first member is movably connected to the secondmember; wherein the first spacer portion is pivotally connected to thesecond spacer portion; wherein the first spacer portion is pivotallyconnected to the second spacer portion by a ball and socket type joint;wherein the ball and socket type joint includes a domed shapedprotrusion extending from the first member and a domed shaped recessformed in the second member.
 23. The surgical cutting guide of claim 22,wherein the second cutting block includes at least one opening extendingtherethrough.
 24. The surgical cutting guide of claim 22 furthercomprising a mechanism for preventing the domed shape protrusion fromseparating from the domed shape recess.
 25. The surgical cutting guideof claim 24 wherein the domed shaped protrusion comprises at least oneindention and the domed shape recess comprises at least one tab andwherein the at least one tab is insertable through the at least oneindention and wherein the dome shaped protrusion is rotatable relativeto the domed shape recess after insertion of the at least one tabthrough the at least one indention to prevent the domed shape protrusionfrom separating from the domed shape recess.
 26. The surgical cuttingguide of claim 22 wherein the first elongated handle is permanentlyattached to the first body portion.
 27. The surgical cutting guide ofclaim 26 wherein the second elongated handle is permanently attached tothe second body portion.
 28. The surgical cutting guide of claim 22wherein the first elongated handle is removably attached to the firstbody portion.
 29. The surgical cutting guide of claim 28 wherein thesecond elongated handle is removably attached to the second bodyportion.